The LIR is now prospectively studying the largest group of patients with the vasculitic syndromes of any center in the world. Clinical, pathophysiologic, immunopathogenic and therapeutic results obtained over the past 13 years have allowed us to design a revised categorization scheme for the vasculitides which has now reached world wide acceptance. We have instituted aggressive chemotherapeutic regimens in several, formerly universally fatal diseases such as Wegener's granulomatosis and have induced cures in 90% or more of these patients. We have now applied these approaches with remarkable success to other of the vasculitic syndromes including systemic vasculitis of the polyarteritis nodosa group, isolated CNS vasculitis, Takayasu's arteritis, and recurrent panniculitis with vasculitis. We have established associations between several of these diseases and various HLA-DR haplotypes. These patient populations have been utilized to precisely delineate aberrations of activation and immunoregulation of lymphoid cell function and have served as excellent models for the concomitant study of normal human immune system. In addition, the precise effects of various therapeutic regimens, particularly corticosteroids and cytotoxic agents, on humna lypmhoid cell activation and immunoregulation have been described.